Ozone has long been recognized as a useful chemical commodity valued particularly for its outstanding oxidative activity. Because of this activity it finds wide application in disinfection processes. In fact, it kills bacteria more rapidly than chlorine, it decomposes organic molecules, and removes coloration in aqueous systems. Ozonation removes cyanides, phenols, iron, manganese, and detergents. It controls slime formation in aqueous systems, yet maintains a high oxygen content in the system. Unlike chlorination, which may leave undesirable chlorinated organic residues in organic containing systems, ozonation leaves fewer potentially harmful residues. There is evidence that ozone will destroy viruses. It is used for sterilization in the brewing industry and for odor control in sewage treatment and manufacturing. And ozone is employed as a raw material in the manufacture of certain organic compounds, e.g. oleic acid and peroxyacetic acid.
Thus, ozone has wide spread application in many diverse activities, and its use would undoubtedly expand if its cost of production could be reduced. In addition, since ozone is explosive when concentrated as either a gas or liquid, or when dissolved into solvents or absorbed into gels, its transportation is potentially hazardous. Therefore, it is generally manufactured on the site where it is used. However, the cost of generating equipment, and poor energy efficiency of production has deterred its use in many applications and in many locations.
On a commercial basis, ozone is currently produced by the silent electric discharge process, wherein air or oxygen is passed through an intense, high frequency alternating current electric field. The discharge process forms ozone through the reaction: EQU 3/20.sub.2 =O.sub.3 .DELTA.H.degree..sub.298 =34.1 kcal
Yields in the discharge process generally range in the vicinity of 2% ozone, i.e., the exit gas may be about 2% O.sub.3 by weight. Such O.sub.3 concentrations, while quite poor, in an absolute sense, are still sufficiently high to furnish useable quantities of O.sub.3 for the indicated commercial purposes.
Other than the aforementioned electric discharge process, there is no other commercially exploited process for producing large quantities of O.sub.3.
However, O.sub.3 may also be produced by the electrolytic process, wherein an electric current (normally D.C.) is impressed across electrodes immersed in an electrolyte, i.e., electrically conducting, fluid. The electrolyte includes water, which, in the process, dissociates into its respective elemental species, i.e. O.sub.2 and H.sub.2. Under the proper conditions, the oxygen is also evolved as the O.sub.3 species. The evolution of O.sub.3 may be represented as: EQU 3H.sub.2 O=O.sub.3 +3H.sub.2 .DELTA.H.degree..sub.298 =207.5 kcal
It will be noted that the .DELTA.H.degree. in the electrolytic process is many times greater than that for the electric discharge process. Thus, the electrolytic process appears to be at about a six-fold disadvantage.
More specifically, to compete on an energy cost basis with the electric discharge method, an electrolytic process must yield at least a six-fold increase in ozone. Heretofore, the necessary highyields have not been realized in any foreseeably practical electrolytic system.
The evolution of O.sub.3 by electroysis of various electrolytes has been known for well over 100 years. High yields up to 35% current efficiency have been noted in the literature. (Current efficiency is a measure of ozone production relative to oxygen production for given inputs of electrical current, i.e., 35% current efficiency means that under the conditions stated, the O.sub.2 -O.sub.3 gases evolved at the anode are comprised of 35% O.sub.3 by volume). However such yields could only be achieved utilizing very low electrolyte temperatures, e.g. in the range of -30.degree. to -65.degree. C. Maintaining the necessary low temperatures, obviously requires costly refrigeration equipment as well as the attendant additional energy costs of operation.
An electrolytic process for the production of O.sub.3 has now been devised which greatly increases the production efficiency of O.sub.3 to an extent sufficiently high to compete with the prior art electric discharge process.